The present invention, in some embodiments thereof, relates to three-dimensional inkjet printing and, more particularly, but not exclusively, to systems, methods and compositions employing ring-opening metathesis polymerization (ROMP) for producing three-dimensional objects.
Three-dimensional (3D) inkjet printing is a known process for building three dimensional objects by selectively jetting chemical compositions, for example, polymerizable compositions, via ink-jet printing head nozzles onto a printing tray in consecutive layers, according to pre-determined image data. 3D inkjet printing is performed by a layer by layer inkjet deposition of chemical formulations, which form together a building material formulation. Thus, a chemical formulation is dispensed in droplets from a dispensing head having a set of nozzles to form layers on a receiving medium. The layers may then be cured or solidified using a suitable methodology, to form solidified or partially solidified layers of the building material.
The chemical formulations used for forming the building material may be initially liquid and subsequently hardened (cured or solidified) to form the required layer shape. The hardening may be effected, for example, by exposing the building material to a curing energy such as thermal energy (e.g., by heating the building material) or to irradiation (e.g., UV or other photo-irradiation), or may be activated chemically, for example, by acid or base activation.
The chemical (e.g., polymerizable) formulations utilized in inkjet 3D printing processes are therefore selected so as to meet the process requirements, namely, exhibiting a suitable viscosity during jetting (thus being non-curable under jetting conditions) and rapid curing or solidification, typically upon exposure to a stimulus, on the receiving medium. For example, when used with currently available commercial print heads, the formulations should have a relatively low viscosity, of about 10-25 cPs, at the jetting temperature, in order to be jettable.
Various three-dimensional printing techniques exist and are disclosed in, e.g., U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334, 7,183,335, 7,209,797, 7,225,045, 7,300,619, 7,479,510, 7,500,846, 7,962,237 and U.S. Patent Application having Publication No. 2013/0073068, all of the same Assignee, the contents of which are hereby incorporated by reference.
In a 3D inkjet printing process such as Polyjet™ (Stratasys Ltd., Israel), the building material is selectively jetted from one or more printing heads and deposited onto a fabrication tray in consecutive layers according to a pre-determined configuration as defined by a software file.
A printing system utilized in a 3D inkjet printing process may include a receiving medium and one or more printing heads. The receiving medium can be, for example, a fabrication tray that may include a horizontal surface to carry the material dispensed from the printing head. The printing head(s) may be, for example, an ink jet head having a plurality of dispensing nozzles arranged in an array of one or more rows along the longitudinal axis of the printing head. The jetting nozzles dispense material onto the receiving medium to create the layers representing cross sections of a 3D object.
In addition, there may be a source of curing energy, for curing the dispensed building material.
Additionally, the printing system may include a leveling device for leveling and/or establishing the height of each layer after deposition and at least partial solidification, prior to the deposition of a subsequent layer.
The building materials may include modeling materials and support materials, which form the object and optionally the temporary support constructions supporting the object as it is being built, respectively.
The modeling material (which may include one or more material(s)) is deposited to produce the desired object/s and the support material (which may include one or more material(s)) is used, with or without modeling material elements, to provide support structures for specific areas of the object during building and assure adequate vertical placement of subsequent object layers, e.g., in cases where objects include overhanging features or shapes such as curved geometries, negative angles, voids, and so on.
Both the modeling and support materials are preferably liquid at the working temperature at which they are dispensed, and subsequently hardened, upon exposure to a condition that affects curing of the materials, to form the required layer shape. After printing completion, support structures are removed to reveal the final shape of the fabricated 3D object.
In order to be compatible with most of the commercially-available printing heads utilized in a 3D inkjet printing system, the uncured building material should feature the following characteristics: a relatively low viscosity (e.g., Brookfield Viscosity of up to 35 cps, preferably from 8 to 20 cps) at the working (e.g., jetting) temperature; Surface tension of from about 25 to about 40 Dyne/cm; and a Newtonian liquid behavior and high reactivity to a selected curing energy, to enable immediate solidification of the jetted layer upon activation (e.g., application of curing energy).
For example, a thin layer (5-40 microns) of the building material should be sufficiently cured within about 200 milliseconds when exposed to UV radiation (of 0.5 W/cm2, 340-390 nm), in order to enable the building of subsequent layers.
When a cured rigid modeling material forms the final object, the cured material should preferably exhibit heat deflection temperature (HDT) which is higher than room temperature, in order to assure its usability. Typically, the cured modeling material should exhibit HDT of at least 35° C. For an object to be stable in variable conditions, a higher HDT is desirable.
Currently, the most commonly used building materials in 3D inkjet printing are photocurable, particularly, UV-curable materials such as acrylic based materials.
Currently available UV-curable modeling material formulations for forming rigid objects by inkjet printing which exhibit the properties required for 3D inkjet printing, while being jetted, as described herein, are acrylic-based materials, which typically exhibit HDT in the range of 35-50° C. Exemplary such formulations are generally described, for example, in U.S. Pat. No. 7,479,510, to the present Assignee.
Such modeling material formulations, when cured, typically feature impact resistance in the range of 20-25 J/m.
While rigid objects, or parts thereof, fabricated by 3D inkjet printing, should desirably exhibit good durability and stability, a cured modeling material should feature both high HDT and high toughness, i.e., impact resistance.
Ring-opening metathesis polymerization (ROMP) is a type of olefin metathesis chain-growth polymerization. The driving force of the reaction is the relief of strained cyclic structures, typically cyclic olefins (e.g., norbornenes or cyclopentenes) or dienes (e.g., cyclopentadiene-based compounds). The polymerization reaction typically occurs in the presence of organometallic catalysts, and the ROMP catalytic cycle involves formation of metal-carbene species, which reacts with the double bond in the cyclic structure to thereby form a highly strained metallacyclobutane intermediate. The ring then opens, giving a linear chain double bonded to the metal with a terminal double bond as well. The as formed metal-carbene species then reacts with the double bond on another cyclic monomer, and so forth.
During recent decades ROMP evolved as a powerful polymerization tool especially due to the development of well-defined transition metal complexes as catalysts. Ruthenium, molybdenum and osmium carbene complexes useful as catalysts of ROMP reactions are described, for example, in U.S. Pat. Nos. 5,312,940, 5,342,909, 5,728,917, 5,710,298, 5,831,108, and 6,001,909; and PCT International Patent Applications having Publication Nos. WO 97/20865, WO 97/29135 and WO 99/51344.
The use of ROMP reactions in reaction injection molding (RIM) has been described, for example, in U.S. Patent Application Publication Nos. 2011/0171147, 2005/0691432, U.S. Pat. No. 8,487,046, EP Patent Application Publication No. 2452958, and EP Patent No. 2280017. One of the ROMP materials used in ROMP-based RIM is dicyclopentadiene (DCPD).
Poly-DCPD-based materials exhibit good mechanical properties and combine both good toughness and high thermal resistance. For example, polymeric materials based on DCPD were used to produce Telene 1810, which features a viscosity of about 200 cps at room temperature, HDT of 120° C. and impact of 300 J/m; and Metton M15XX, which features a viscosity of 300 cps at room temperature, Tg of 130° C. and impact of 460 J/m [see, for example, www(dot)metton(dot)com/index(dot)php/metton-lmr/benefits].
Additional background art includes WO 2013/128452; Adv. Funct. Mater. 2008, 18, 44-52; Adv. Mater. 2005, 17, 39-42; and Pastine, S. J.; Okawa, D.; Zettl, A.; Fréchet, J. M. J. J. Am. Chem. Soc. 2009, 131, 13586-13587; Vidaysky and Lemcoff, Beilstein J. Org. Chem. 2010, 6, 1106-1119; Ben-Asuly et al., Organometallics 2009, 28, 4652-4655; Piermattei et al., Nature Chemistry, DOI: 10.1038/NCHEM.167; Szadkowska et al., Organometallics 2010, 29, 117-124; Diesendruck, C. E.; Vidaysky, Y.; Ben-Asuly, A.; Lemcoff, N. G., J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 4209-4213; Wang et al., Angew. Chem. Int. Ed. 2008, 47, 3267-3270; U.S. Patent Application Publication No. 2009-0156766; WO 2014/144634; EP Patent No. 1757613 and U.S. Pat. No. 8,519,069.